#![allow(unused_variables)]

type File = String;

fn open(f: &mut File) -> bool {
    true
}
fn close(f: &mut File) -> bool {
    true
}
#[allow(dead_code)]
fn read(f: &mut File, save_to: &mut Vec<u8>) -> ! {
    //不返回数据
    unimplemented!() //执行该宏程序崩溃
}

fn main() {
    let mut fl = File::from("fl.txt");
    open(&mut fl);
    close(&mut fl);
}
